The present invention relates to a method for optimizing the gear-shifting sequences in a step-variable transmission, in particular an automated shift step-variable transmission for motor vehicles.
In automated shift transmissions (AST) the shift clutches of the step-variable transmission and a drive-away and disconnect clutch on the input side are operated by way of actuators. The actuators may be driven by an electric motor or fluidically driven, for example. The actuators are coordinated by a control unit. Gear changes may be initiated both manually and fully automatically according to an overriding gear shifting strategy.
The time taken to shift gear is particularly important in the case of ASTs, since a gear change is generally accompanied by an interruption or at least a reduction of the tractive force. In the case of an AST a gear change involves the disengagement of an initial gear or original gear and the engagement of a target gear.
The shift clutches (or simply clutches) used for engagement and disengagement of the gears primarily serve to produce a positively interlocking connection, which sets up the respective gear. The clutches frequently take the form of synchronizer clutches, which have a further function in that they serve for synchronizing the rotational speeds when engaging a gear. In a synchronizer clutch the synchronization point is represented by the position of a gear-shifting member of the synchronizer clutch at the commencement of the rotational speed matching. The synchronization position is the position on completion of the rotational speed matching.
The publication DE 101 10 898 A1 discloses a method for the commissioning of an AST. In this case the transmission parameters needed for selection and shifting are determined before fitting the step-variable transmission into a vehicle and are stored in a control unit. This is intended to have the advantage that the transmission parameters required for subsequent operation can be determined by means of external sensors prior to fitting, in order to compensate for standard deviations occurring in series production. This is also intended to lead to a high degree of accuracy in determining the synchronization positions of the individual gears. Transmission parameters are here taken to include the geometric data of the internal gear-shifting members of the transmission, the position of limit stops in the transmission etc.
For registering (detecting) the synchronization position of a synchronizer clutch in the known method the transmission input shaft is made to rotate by an external drive before the transmission is fitted. The synchronization position is then approached. The variation in the speed of the input shaft is monitored. Attainment of the synchronization point (referred to there as the synchronization position) is established when a variation in the rotational speed exceeds a predetermined threshold. Here a gearshift sleeve for the engagement of the relevant gear is to be actuated slowly and under a low force by the respective actuator.
Alternatively it is also possible to apply an input torque to the transmission input shaft and to monitor the output torque. Attainment of the synchronization point is established when a variation of the output torque exceeds a predetermined threshold.
DE 103 12 400 A1 further discloses an adjustment of the voltage of an electric motor used as actuator in running to the synchronization point, so that in running to the synchronization point at constant speed the precise synchronization force is achieved.